This invention relates to vane pumps and more particularly to vane pumps incorporating undervane pumping.
In general, the typical vane pump does not incorporate an undervane pumping feature. However, those pumps embodying this feature have no provision for balancing the pressure forces in the seal arcs between the inlet and discharge ports. Unless the vanes are sufficiently heavy, such pressure forces can overcome the centrifugal forces in the seal arcs, thereby causing the vanes to depart from engagement with the cam surface.
Many existing vane pumps employ pressure loaded sideplates to compensate for thermal expansion. Usually, this mandates the use of highly wear resistant materials, such as tungsten carbide, for the vanes and sideplates and begets attendant manufacturing difficulties. In addition, the ends of the rotor do not readily lend themselves to the inclusion of a thrust carrying bearing owing to the sliding engagement between the vane ends and the sideplates and the small length lands between the vane slots with sharp corners. It will be appreciated, for the above reasons, that the ends of a conventional rotor are not ideally suited to supporting a hydrodynamic lubricating film and are, therefore, limited in their load carrying capacity.